The present invention relates to a high current ion source and, in particular, to a source for generating ion beams from nonvolatile materials.
Radiation in the form of charged ions beams of about 10 to 100 mA current intensity are used for the operation of mass separators and ion implantation systems. In heavy ion accelerators, the final intensity can be increased if a high current source of singly or multiply charged ions is used, ions of nonvolatile elements and apparatus for their generation being of particular interest.
A mass separator source has been disclosed in the publication Ion Implantation, G. Dearnaley et al, North Holland Publ. Comp., Amsterdam (1973) pages 324-328, wherein a heated filament is arranged exactly in parallel with and at a predetermined distance from an extraction slit, the width of the extraction slit being correlated with the position of the filament. This apparatus permits the generation of ion currents up to 10 mA. However, it is disadvantageous in that the ion beam has a narrow rectangular cross section, the ion source burns quietly only within narrowly defined operating parameters and oscillations occur which destroy the space charge compensation of the ion beam and produce high divergence. Further, the plasma density cannot be adapted to a predetermined, freely selectable extraction geometry and the ion current cannot be increased by enlarging the extraction surface. Other disadvantages of the prior art mass separator source are that increasing the length of the slit requires a large heating filament which tends to warp during operation, the source body is made in part of graphite into which the charge material diffuses, the insulators are freely exposed to contamination by the generated vapor, the source must be built into a relatively large vacuum vessel and an external, homogenous magnetic field is necessary.
It is an object of the present invention to develop a high current ion source with which ion beams of high current intensities and predetermined beam cross-sections can be generated, and which can be adapted to predetermined operational requirements.